Double demodulation receiver



-26,1930. 8. WASHINGTON 1,174,493

DOUBLE DEIIODULATION RECEIVER Filed Jan. 3, v1927 2 Shoots-Sheet 1 I I I II I MI I 5min: Gaurna;

6, 1930. B. WASHINGTON 1,774,493

DOUBLE DEMODULATION RECEIVER Filed Jan. 3, 1927 2 Shuts-Sheet 2 Patented Aug. 26, 1930 U ET-ED STATES PATENT OFFICE BOWDEN WASHINGTON, OF NEW YORK, N. Y., ASSIG1\TOR OF ONE-HALF TO HAZEN Li- HOYT, JR., OF NEW YORK, N. Y.

DOUBLE DEMODULATION RECEIVER Application filed January 3, 1927. Serial No. 158,648.

.The main object of my invention is to produce a sensitive and selective radio receiver for the reception of continuous waves, interrupted continuous waves, or damped group 5 transmission.

Another object is to produce a receiver wherein after a high degree of amplification has been attained at one frequency, the signal may be shifted to a different frequency and 10 re-amplified before final demodulation and conversion to an audible frequency.

It is well known that even if a considerable number of precautins',fsuch as shielding, neutralizing or balancing, battery line by- 15 pass condensers and chokes, etc, are used, it

is extremely difiicult-to amplify beyond a certain point at any given frequency on account of the fact that with a high over all I amplification an extremely small amount of 20 over all feed back willcause instability and oscillation. 1 V

In my receiver by detection and a change of frequency in a novel manner, a very much larger amplification can be effected without 2 'the use of alarge number of precautionary measures. 1

Referring to the drawings, Fig. 1 is a schematic wiring diagram of a receiver embodying my invention. y 30 Fig. 1? is a schematic diagram showing a modification of the apparatus for changing the received carrier frequency into a lower carrier frequency.

Fig. 2 is a diagrammatic perspective draw- 35 ing of one form of rotary variable inductance,

such as is used in my invention.

Fig. 3 shows another form of rotary variable inductance and Fig. 4 shows a third form with a part of its associatedcircuits.

In the embodiment shown in 1 the antenna (of any form). is connected through the inductance 11' to the ground 12. This inductanceforms the primary of a radio frequency transformer whose secondary '13 '45 is tuned by the variable condenser 14.

In parallel with this condenser are connected the gridc15 and cathode 16 of the vacuum tube 17. .The anode 18 of this tube v is connected through the delivery inductance V, 50 19 and the anode voltage source 20 to the cathode 16. The closed resonant circuit 21 comprises the inductances 22 and 23 and the variable condenser 24. The inductance 22 .is coupled to the delivery inductance 19 of the tube 17 and therefore need not be described" the grid circuit inductance 25 of the tube 26. The immediately associated amplifier circuits of the tube 26 are identical with those of the tube 17 and therefore need not be described indetail. The circuit 27 is also identical with the circuit 21. I I

The closed resonant circuits 21 and 27 interposed between the amplifier circuits containing vacuum t-ubes 17 and 26 if properly designed, add to the selectivity of the receiver with little or no loss of amplification, and also tend to electrically separate the circuits containing tubes, thus aiding in the suppression of oscillation and instability. It is preferable that the condensers 24 and i 28 be operated by a single control as disclosed for instance by the Hogan U. S. Patent #1,014,002 and thecondensers 14, 29 and 30 may also beso' operated thus reducing the tuning controls to two.

The circuit 27 delivers the amplified radio frequency energy to the detector circuit 31. This circuit contains the inductance 32 coupled to resonantcircuit 27, the variable condenser30, and inserted between these two elements the rotary variable inductor schematically shown at 33. This device, several forms of which are later described, changes the period of the circuit 31 into and out of resonance with thepreceding circuits at a chosen frequency which may be of the order of 5000 times per second, thus varying the input to the detector and consequently its output ata corresponding rate or frequency. The outut or anode circuit ofthe detector contains the inductance 35 and the capacity 36 which elements form a branch circuit which is preferably resonant to the frequencyat which the detector output is varied by the rotary variableinductance 33. This rotary inductance may preferably be driven by either a synchronous motor or a motor equipped with ordinary tuning fork speed control.

The signals after detection produceoscillations of a chosen intermediate frequency in the circuit containing the inductance and the condenser 36. The frequency of these oscillations is dependent on the construction and speed of rotation of the rotary variable inductance 33.

The inductance 35 is coupled to the inductance 37 in the grid-cathode circuit, of the tube 38. The anode-cathode circuit of this tube contains the primary of a suitable ine mediat f equ ncy transformer 39 whose secondary is in the grid-cathode circuit of the tube 40. This tube is in turn coupled in a similiar manner to the tube 41.

The anode-cathode circuit of the tube 41 contains the inductance 42 which is coupled to the inductance 43. This inductance 43 together with the rotary variable inductance 44 and the condenser 45 form the closed resonant input circuit of the detector 46, and this circuit is so proportioned that during the variations of inductance of the rotary inductor 44 it will come into and out of resonance with the chosen intermediate frequency at a suitable audio frequency rate, thus varying the input energy and therefore the output energy of the detector at a chosen audio fre quency. The output or cathode-anode circuit of the second detector 46 contains a suitable oerceptive instrument such as the telephone receiver 47 and the anode battery 20 A suitable audio frequency amplifier of one or more stages may of course be added but was omitted from the drawing for the sake of simplicity.

The rotary variable inductor 44 may be of a similar construction to the variable inductor 33 but suitably designed for varying its inductive value at a suitable tone frequency, such as 500 a second. The speed of its driving motor is preferably variable within cert ain limits so. that the operator may vary the tone frequency of the signals to avoid ear fatigue. When receiving group transmission the rotary variable inductor is not rotated but is allowed to remain stationary in a position such that the circuit in which it is in- Qllldcd resonant tothe intermediate frequency A common cathode heating battery is shown at 48 with controlling rheostat at 49. Separate anode batteries as 20, 20, 20 and 20?, are shown but it is understood that a common (battery; could be substituted.

"In both detector circuits grid leaks are shown at 50 and 50 and grid condensers at 51 and 51." but it should be understood that detection by operating along a kink in the characteristic of a partially gaseous tube may be employed.

Fig. 2 is a diagrammatic illustration of one formof rotary variable inductance such as is shown #33. Fig. 1. In this form the stator carries mounted upon its inner face the pole coils as 7.1, 71; and 71. and is faced by the'rator carrying an equal number of coils at 73, 73 and 73". Current may be brought to the rotor coils by the brushes 74 and 7 4 and collector rings 75 and 75 mounted on the shaft 76 of the driving motor 77. The rotor windings and the stator windings may be connected in series or parallel or in any combination which will give the desired inductance variation.

In the form of inductor such as is shown in Fig. 2 a gain may be made in frequency of variation of inductance though at a loss of amplitude of variation by so constructing the device that the number of rotor coils differs from the number of stator coils preferably by one. This greatly reduces the speed and size of the device. A combination of a 9 pole stator and a 10 pole rotor driven at 3000 R. P. M. would give a variation frequency of the order desired or approximately 6,000 a second.

It should be noted that if the circuit containing the rotary inductor is so adjusted that resonance is attained when the inductance of the rotary inductor is half way between maximum and minimum the frequency obtained by detuning will be twice that obtained when resonance occurs at either extreme of inductance variation.

Fig. 3 shows another rotary variable inductance construction. The stator 80 and its polecoils 81, 81 and 81 may be of similar construction to the 1 stator shown and described under Fig. 2 but in this case the variation of inductance is caused by the change of fluX-path-area obtained by the rotation of the toothed rotor 82 which is preferably constructed of copper or other metal of high conductivity.

In the operation the signal energy is collected by the antenna filtered and amplified by the tube 17 and as associated circuits, further filtered by the circuit 21, further filtered and amplified by the tube 26 and its asso ciated circuits filtered again by the circuit 27 and then delivered to the circuit containing the tube 34 for detection and modulation to an intermediate frequency. Assuming the signal to be a continuous wave of a frequency of 200,0 00cycles when the receiver is properly tuned a current of this frequency will flow in the circuit 27 which is inductively coupled to the inductance 32 which is included in the periodic grid-cathode circuit 31' of the first detector tube 34. This circuit also contains the rotary variable inductance 33 which is so designed as to vary the periodicity of the circuit several thousand times a second, and as this circuit 31 comes into resonance with the circuit 27 a large amount of 200,000 cycle energy will be detected by the tube 34, while on either side of resonance the detected energy will be greatly diminished if not brought substantially to zero. We have therefore a detected current in the anode-cathode circuit of he diame er t be 4 v yi g ts. inten ty at a frequency which we shall choose, say 6000 periods a second. The circuit containing the inductance 35 and the condenser 36 is preferably resonant to this frequency and the inductance 35 delivers 6000 cycle energy to the grid inductance 37 of the tube 38. This 6000 cycle energy is amplified by the tubes, 38, 40 and il and their associated circuits and finally delivered to the detector tube 46 by the coupling existing between the inductance l2 and 43. The period of the grid-cathode circuit ofthe tube 46 is varied above and below 600 cycles at a suitable audio frequency rate such as 400 cycles by the rotary variable inductor 44 thus modulating and making clearly audible the detected energy in the output circuit of the tube l6. I

This receiver is primarily designed for use in commercial radio telegraphy such as ship to shore and point to point communication when the results attained far outweigh considerations such as cost or seeming elaboration of apparatus. By means of my invention great selectivity and high amplification may be had in the circuits resonant to the received wave frequency plus an equal or greater amount of amplification at the chosen intermediate frequency, thus producing a receiver of extreme sensitivity and selectivity which is easy to control both manually and insofar as objectionable tube oscillations are concerned.

In Fig. 4: the variation of the period of the circuit containing the inductance 32 and the condenser 30 is effected by coupling to this inductance an inductance 8 l'which may be periodically short-circuited at the desired frequency by the commutator and the brushes 86 and 87 thus changing the effective value of the inductance 32 and hence the period of the circuit.

lhe change of the received carrier fre quency into a lower or intermediate carrier current frequency maybe efi'ected by a rotary device 33' (Fig; l mechanically'similar to that shown in Fig. 2 but which is electrically connected so as tovary the coupling between the circuits 27 and 31 at such a rate as to pro duce the desired intermediate frequency.

I claim:

1. In a radio receiver, a plurality of tuned radio frequency amplifiers and a plurality of periodic circuits interposed between said amplifiers, a first detector, a periodic detector input circuit associated with the output of said radio frequency amplifiers, a rotary variable inductor whereby the periodicity of saiddctector input circuit is variable from the frequency of the received wave to a frequency relatively high in comparison to the usual audio signal frequencies, a plurality of fixed frequency amplifiers adapted to amplify electrical currents of a frequency corresponding to the frequency of said varied periodicity, the input of said amplifiers being associated with the output circuit of said first detector, a second detector having a periodic input circuit, theoutput of said fixed frequency amplifiers being associated with the periodic input circuit of said second detector the periodicity of the second detector varying from the frequency of variation of period of the input circuit of the first detector at a rate corresponding to a highly audible frequency.

2. In a radio receiver, a plurality of tuned radio frequency amplifiers and a plurality of periodic circuits interposed between said amplifiers, a first detector associated with the output of said amplifiers, a periodic detector input circuit having a constant speed rotary inductor associated therewith Whose periodicity is variable from the frequency of the received wave to a frequency relatively high in comparison to the usual audio signal frequencies, a plurality of fixed frequency amplifiers adapted to amplify electrical currents of a frequency corresponding to the frequency of said varied periodicity, the in put of said amplifiers being associated with theoutput circuit of said first detector, and a second detector the output of said fixed amplifiers being associated with the input circuit of said second detector.

3. In a radio receiver, means for selecting and amplifying any frequency within a predetermined band, a detector, a constant speed rotary variable inductive means for varying the power delivered from the selecting and amplifying means to the detector at a frequency higher than the common tone frequencies, said rotarymean-s being associated with the tuned output of the selecting and amplifying means, means for amplification ofenergy from the detector at said lower carrier frequency and means for indicating the presence of said energy after amplification.

4. A radio receiver having amplification at two differing carrier frequencies, said amplification occurring before final demodulation, the first of said carrier frequencies being the 7 carrier frequency of the received wave, means for changmg the said signal carrier frequency to a lower and substantially inaudible carrier frequency, said means including a demodulator having a tuned input circuit whose tuned constants are varied at the said substantially inaudible rate, and means for further amplification at said substantially inaudible rate.

- 5. The method of amplification and selection of a received radio signal which consists in" alternately selectively amplifying and selectively coupling said amplifying means at the received carrier frequency, converting saidainplified and selected carrier frequency to a lower carrier frequency by detection in a periodic circuit whose period is varied so as to vary. the detector, input at afrequency which will produce said lower carrier frequency, further amplifying at said lower carrier frequency, and rc-detecting.

6. A method of amplifying a received radio signal at a carrier frequency other than that of the received signal consisting in coupling a circuit containing the carrier frequency of the received signal to a variable periodic circuit containing a detector which circuit is varied into and out of resonance with the received carrier frequency at a frequency which will cause the detector output to consist of a new and lower carrier frequency and then amplifying and redetecting said lower carrier frequency.

7. A method of amplifying a received radio signal at two difierent carrier frequencies consisting of first amplifying at the received carrier frequency, detecting the amplified signal, then varying the amplitude of the detected signal by bringing a )BIlOCllC detector input circuit into and out of resonance with said received carrier frequency cyclicly at a rate which will produce a new and lower carrier frequency in the output of said detector, amplifying further at said lower carrier frequency and re-detecting the amplified signal.

8. The method of amplification and selection of a received radio signal which con sists in alternately selectively amplifying and selectively coupling said amplifying means at the received carrier frequency, converting said amplified and selected carrier frequency to a lower carrier frequency by varying the period of a periodic detecting circuit so as to vary the detector input at a frequency which will produce said lower carrier frequency in the detected output, further amplifying at said lower carrier frequency, and re-detecting.

9. A receiver comprising means for collecting radio signals, means for amplifying and selecting said signals at their transmitted carrier frequency, means for changing said carrier frequency to a lower carrier frequency, said means consisting of a demodulator and means in the input circuit of the demodulator for varying the constants of said input circuit at the rate corresponding to the said lower frequency, means for amplifying said lower carrier frequency, and means for producing an audible signal from said latter carrier frequency ineluding a demodulator whose input circuit tonstants are changed at an audible rate.

;' 10. A radio receiver having amplification 'at two carrier frequencies comprising means for amplifying and means for selecting signals within a predetermined band of frequencies, a first detector having a periodic input circuit and an outputcircuit, means for periodically varying the constants of said input circuit at a substantially inaudible rate so as to produce a lower signal carrier frequency y BOl/VDEN WASHINGTON. 

